1. Field of the Invention
This invention relates to a pressure swing absorption chamber, and more particularly to an oxygen concentrator system having a multi-chamber canister for receiving compressed air from a compressor and directing the air through a series of chambers integral within a single assembly for producing concentrated oxygen in a pressure swing absorption system, which system provides 10 LPM at an oxygen concentration of at least 93%.
2. Description of the Related Art
Adsorption separation processes depend on the ability of certain solids to selectively adsorb one or more components from a gaseous mixture. In oxygen concentrators for patient use, the adsorption separation processes are usually fixed bed operations, including two main steps, the adsorption step and the desorption step.
Pressure Swing Adsorption (PSA) is a useful technique for separating components of gaseous mixtures in such medical uses. A gaseous mixture, typically ambient air, is fed into a chamber, where the species are separated, producing a stream with a high percentage of one component. Air contains many species, namely approximately 21% oxygen, 78% nitrogen, 0.9% argon and 0.1% other trace gases. PSA can be used to separate the oxygen from the inlet air, to supply the patient with higher concentrations of oxygen.
Generally, such species separation in the chamber is achieved by using a zeolite, or molecular sieve, which has a selective affinity for adsorbing a certain component in the mixture. Zeolites are natural or synthetically produced molecular sieves that have uniform pores or crystalline cavities. Chemical species small enough to fit into the zeolite's pores are adsorbed onto the surface of the zeolite material. How readily a species adsorbs onto the zeolite depends on the shape and size of the molecule compared to the shape and size of the pores in the zeolite pellet. A zeolite can adsorb a molecule of any diameter up to its own pore size.
Pressure Swing Adsorption relies on swings in pressure to cycle the chamber sequentially from selective adsorption to desorption. This swing can occur from high pressure to atmospheric pressure or from atmospheric pressure to vacuum. If the swing occurs from atmospheric pressure to vacuum, it is technically considered Vacuum Pressure Swing Adsorption (VPSA). It is well know to those of skill in the art the PSA and VPSA techniques for species separation are quite different, each technique with its own attendant benefits and deficiencies.
A typical pressure swing absorption system is an oxygen concentrator that separates the oxygen from air for subsequent inhalation by a patient. Conventional systems provide 5 liters per minute (LPM). Such oxygen concentrators include a plurality of molecular sieve beds for separating the gas into an oxygen and a nitrogen fraction whereby the oxygen is subsequently provided to a patient while the nitrogen is retained in the sieve bed and subsequently purged. These oxygen concentrators include several components such as an air compressor, two three-way air valves, multiple canisters each housing a separate molecular sieve and a product reservoir tank. Such structures require extensive valving and plumbing which affects the efficiency and costs of these systems.
U.S. Pat. No. 5,997,617 to Czabala et al. discloses an improvement in the art of 5 LPM pressure swing absorption system that incorporates a multi-chamber canister assembly for improving both the efficiency of the system, and the cost of the system. The assembly minimizes the temperature difference between molecular sieves due to their location within the canister, and provides a system wherein multiple operations of the pressure swing absorption system are incorporated within a single housing assembly.
The Czabala et al. PSA system includes a multi-chamber canister for a pressure swing absorption system which includes at least three chambers. The canister includes a housing of a general length. A first molecular sieve chamber is disposed within the housing for receiving a first molecular sieve for separating air from the ambient environment into a concentrated gas component. At least a second molecular sieve-chamber is also disposed within the housing for receiving a second molecular sieve for separating air from the ambient environment into a concentrated gas component. A supply chamber is disposed within the housing for receiving air from the ambient environment and for communicating the air to either the first or second molecular sieve chamber.
When those of skill in the art approach the problem of “scaling-up” a Czabala et al.—like device to deliver in the range of 10 LPM, they have, prior to the present invention, simply attempted to design such systems with double the sieve material, and double the air flow, to provide double the resulting 5 LPM of oxygen. Yet, the additional sieve material weight and volume in such an approach results in a device of a size and weight that is disadvantageous not only to the market, but to the patient as well in view of price, noise, size, weight and power consumption.
An example of such a device is the INTEGRATEN™ by SeQual. This concentrator is marketed as a 10 LPM, but suffers from basically a doubling of SeQual's 5 LPM unit. Further, it utilizes at least twelve individual chambers, sequentially directing the flow of compressed air to a group of four sieve beds (adsorption), while at the same time another four beds are purged into the atmosphere through the valve (desorption). The remaining four of the twelve beds are interconnected through the valve to equalize pressure as the sieve beds sequentially transition between adsorption and desorption. Thus, not only does the unit have an overabundance of chambers, it is nearly twice the weight, nearly twice the size, and uses nearly twice the adsorbent material of the 5 LPM device to provide up to 10 LPM. Further, the oxygen concentration from ½ to 7 LPM is only 93.5% (±1.5%), and from 7 to 10 LPM is only 92% (±3%).
The INTEGRATEN™ has some disadvantageous specific performance ratios. For example, the INTEGRATEN™ is 4.22 ft3, and thus has a specific unit size per LPM=0.422 ft3/LBM when providing 10 LPM. Further, this unit has a weight of 57 lbs., and thus has a specific unit weight per LPM=5.7 lbs./LBM when providing 10 LPM.
Thus, while the Czabala et al. system is beneficial, and is efficient in the 5 LPM range of operation, and the INTEGRATEN™ by SeQual provides up to 10 LPM in a scaled-up version of their 5 LPM unit, it would be desirable to provide a PSA system that could deliver high output in the range of 10 LPM in a two chamber system, and deliver a reliable oxygen concentration of 93% or more at 10 LPM, all in a system that has similar weight, size, sound level and power consumption characteristics as the Czabala et al. system. It is to such an oxygen concentration system that the present invention is primarily directed.